I see this developer forum is quite abandoned, I just hope I get response.
Searching for mails with attachments seems to return wrong mids:
SELECT * FROM ymail.search WHERE attachmentcount-min="1"
returns messages filtered properly, but it gives mids like this :
While it seems proper it turns out to be wrong, because manually searching the ymail.messages table for the corresponding message has the mid : 2_0_0_1_8697_AK/tHkgAALa3UYfj3QbCVCHBFb8